Radio-frequency identity tags (“RFID”) are currently constructed with metallic coils and a silicon chip. They are used, for example, for logistical purposes, access controls or the like. RFID tags are intended to operate as passively as possible, without a battery. Energy is drawn from a coil that is activated by a resonating reader. In this manner, a memory in an electronic chip of the tag is activated and a stored item of information is read out, such as an identification of sender and an addressee in the case of logistical applications. On account of their relatively high production costs, RFID tags are not cost-effective for use in mass applications, such as for electronic bar coding, for protection against copying or cloning or for use in disposable articles.
The operable range of distance between the reader and the tag is determined in part by the power of radiation of the reader occurring at frequency ranges such as 125 kHz or 13.56 MHz, and is also determined by the size and quality of the coil or antenna of the tag. In the case of passive tags, this range is typically less than 60 cm. The construction of the coil in this instance depends greatly upon the carrier frequency used. For example, a wound coil with generally several hundred turns is used at a frequency of 125 kHz, while a flat coil of approximately ten turns is used in the case of a frequency of 13.56 MHz.
An example of a known organic field-effect transistor is provided in DE 100 40 442.1. Organic electronic circuits can be produced at very low cost. They are therefore suitable for the construction of tags that can be used in mass markets and with disposable products. Other conceivable applications include electronic tickets, electronic postage stamps, electronic watermarks, and applications for protection against theft or for baggage control.
Unfortunately, electronic circuits that are comprised of organic material are associated with two major disadvantages. First, organic materials are very sensitive to environmental influences, such as light, air and water, and age relatively quickly under this influence. Second, antennas produced by a polymer technique, or by any printing technique, are distinctly inferior to metallic antennas. The antennas have a higher electrical resistance and are of lower quality. As a result, such electronic components and tags based on organic materials have only a short service life and are suitable only for a very short range.
The problem concerning durability is comparable to that associated with organic light-emitting diodes, known as OLEDs. Presently, glass is used as the substrate for these diodes, and a glass plate is also adhesively attached over the components to ensure a good hermetic encapsulation. However, for mechanical reasons and reasons relating to cost, glass is not possible for the type of applications for which the present invention is generally directed. Conventional organic substrates are permeable to light, air and water and consequently are likewise not suitable. Metallized substrates, such as are used for example in the food packaging area or for the airtight packaging of sensitive materials, likewise do not come into consideration for RFID tags in particular, since the metal layer in the substrate prevents coupling of the coil to the reader. A Faraday cage or metallic shielding is created.
Accordingly, a substantial need exists for organic electronic circuits that are not especially sensitive to environmental influences and do not have problems associated with durability.